Checkout Spinning and Not Working

About a year ago I had a similar issue and the tech staff help me get it sorted now I am back.
When *Logged OUT*, checkout doesn't work. Gives the following JS error in console:
TypeError: a is undefined
http://www.silverstreetstudios.co.uk/my/wp-content/plugins/marketpress/ui/js/jquery.validate.min.js
We have done a plugin and theme conflict test and it didn't solve the issue.